Many people who die of opioid overdoses got addicted to the drugs after they were prescribed for common problems.

This study included 861 doctors in San Diego County who prescribed opioids to 170 patients who died of an overdose within a year.

The doctors were divided into two groups. One group got a personal letter from the county's chief medical examiner that identified the patient who died of an overdose. It also included information about prescription drug deaths in their area, as well as safe-prescribing guidelines. The other doctors got no letter.

Over the next three months, doctors who received the letter wrote nearly 10 percent fewer opioid prescriptions. Doctors in this group also ordered fewer high-dose opioids and wrote fewer opioid prescriptions for patients who'd never taken them before.

There were no changes in opioid prescribing by doctors who did not receive the letters, according to the study in the Aug. 10 issue of the journal Science.

The study was led by Jason Doctor, chair of the department of health policy and management at the University of Southern California's Price School of Public Policy.

The prescription decline triggered by the letters was greater than that achieved by limits on opioid prescribing, which suggests such letters may be an effective tool in fighting the opioid epidemic, according to the authors.